Addressing and routing in wireless mesh networks

ABSTRACT

The present invention is directed to a method and apparatus for forwarding and/or addressing a packet in a wireless network, wherein an address information of a protocol layer lower than a network layer is added to the packet, which address information indicates the geographical location of a destination node and which can be changed during forwarding of the packet through said wireless network. The packet is then forwarded within the wireless network based on a difference between the geographical location of a present node and the destination node. This location based addressing makes packet forwarding easier in dynamic mesh networks, because each node ( 10 ) can decide into which direction to forward incoming packets based only on the information in the packet header and its own location.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for addressingand/or routing in a wireless mesh network.

BACKGROUND OF THE INVENTION

Wireless broadband networks make high performance Internet accesspossible where wired broadband infrastructure is impractical. However,such a wireless broadband network will only be a success especially forresidential and small business markets if the infrastructure is providedat a low cost, is robust to changing environments, easy to deploy andscalable with market demand.

New wireless networks with wireless routers as network nodes on a meshnetwork basis emulate the topology and protocols of the Internet but areoptimized for wireless high-speed data transmission. Such mesh networkconsists of wireless routers connected to each other with radio links.The radio links are able to arise and break down and the network is ableto adjust itself to the current condition of the radio links. Alsoindividual devices can be switched on and off without disturbing thenetwork functionality excessively. The routing protocol keeps track ofthe whereabouts of the nodes in the network thus making it possible toroute packets between distant nodes using the other nodes in the networkas an intermediate nodes. Currently there exists several routingprotocols that can be used in mobile mesh environment.

The routing protocols are able to handle small amounts of mobility.Still, problems arise when the majority of nodes are mobile, becauseevery node has to know whereabouts of every other node in some extent.This becomes a more serious problem when mesh networks get largerbecause the changes in the network structure have to be informed tobigger amount of nodes and because the number of changes in the networkis of course the higher the bigger the network is. Also the routingtables get bigger and bigger if the mesh gets larger because the routesin the network cannot be aggregated in the same way as in traditionalwired networks.

FIG. 1 shows a wireless mesh network (WMN) comprising several wirelessrouters WR connected via radio links. Not all wireless routers WR heareach other. Hence, packets between two wireless routers WR in the sameWMN might have to be forwarded via several wireless routers WR andwireless links before reaching the destination. A wireless router WR canalso have other interfaces than those to the mesh network, e.g. WLAN,Ethernet and/or Bluetooth interfaces, to which other network devices areconnected. Furthermore, there may also exist routers having othersub-networks with laptops LT, wired routers R and servers SV. One ormore of the wireless routers WR may act as an AirHead AH arranged toconnect the WMN to other larger networks, e.g. to the Internet.Terminals such as laptops LT may also include wireless routerfunctionality, i.e. they may act as a part of the WMN.

WMNs suffer from constantly changing conditions, which cause links tofail and reborn according to the current conditions. They may not haveany specific administrator to take care of the networks, which meansthat they have to be self-organizing and self-healing. In WMNs, thewireless routers WR can also move, which means that the networkstructure is changing all the time.

Currently, the existing mesh networks are quite static with mostlyfixedly mounted wireless routers WR, but in the near future also cars,trains, buses and other public transport devices may join the WMNs. Inthe wildest visions, all the people walking on the streets have theirown small wireless router WR in their pocket and the whole networkconsists of these privately owned devices. In this kind of situation,the network structure is changing really fast and there is no way ofkeeping track of the exact location of every device. Also the size ofthe WMN in both the number of wireless routers WR and the surface areamay be quite huge. In extreme cases one WMN may cover the whole world.This means that the methods proposed to be used in future WMNs have tobe as scalable as possible so that they can be used efficiently nomatter how large the networks will be. The large address space of thenew Internet Protocol version 6 (IPv6) makes it possible to use the IPprotocol in this new environment. However, because the IP addresses ofthe routers cannot be changed on the fly easily without breaking theconnections, this is not an optimal solution for the mobile wirelessnetworks. The address changing on-the-fly would be needed in order topreserve the route aggregation in the IP networks.

New routing protocols have been developed especially for wirelessnetworks with no fixed topology. These protocols try to decrease theamount of the routing traffic needed by not telling other nodes aboutthe less important changes in the network structure. However thelocation of other nodes has to be known to some extent in order to beable to forward the traffic to the right direction. These protocols workquite fine when the network structure remains the same and only theradio quality of the links changes a little. But when the routers startto move, the usable network capacity collapses because of the routingprotocol updates and the packets not finding their destinations.

The mobile IP protocol solves the terminal mobility problems that arecaused by mobile terminals changing their location in the network. Itchanges the mobility problem into a routing problem hence not solvingthe mobility problems in the wireless mesh networks, where also therouters are able to move and where the main problems are actually in therouting area.

Furthermore, traditional MAC (Medium Access Control) switching in fixedwired networks is based on learning the MAC addresses from the sourceMAC addresses of the packets coming in from an interface. It alsorequires that broadcast and multicast packets have to be repeated toevery link. This method works fine in the traditional fixed wirednetworks, but in WMNs it cannot be used, because of the differentnetwork structure and the network capacity wasted because of thebroadcasts.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand apparatus for providing an addressing and/or routing function indynamic wireless mobile mesh networks.

Accordingly, a location based lower level (e.g. link layer, layer 2, orMAC layer) addressing is provided which is quite handy in networks withmesh-topology where the routing nodes are also capable of moving. Thelocation based addressing makes packet forwarding easier in the networkbecause each node can decide into which direction to forward incomingpackets based only on the information on the packet header and their ownlocation. This means that nodes do not need to maintain big routingtables and make time-consuming searches to those tables that are goingto be really huge in big mesh networks. It is thus possible to changethe addresses based on global position on the fly without breaking theconnections and/or causing tremendous routing information update needs.This is possible because it is not necessary to change the higher layer(e.g. network layer, layer 3 or IP layer) address when the equipmentmoves inside the mesh, because the packet forwarding in the network ismade based on the lower layer addresses. Instead, the lower layeraddress of the device is changed when it is moving, while the higherlayer address is kept unchanged. If the location is changed to anothernetwork, higher layer methods, such as Mobile IP, can be used.

Location based lower layer addressing also makes it possible to carryout the packet forwarding in mesh networks on link layer, which issimpler and faster compared to the situation where every packet has tobe processed on the higher layer.

With this method the routing information needed to be exchanged in thenetwork is minimized. This means that when the equipment is switched on,it can almost immediately start communicating through the network, whichis impossible with earlier solutions because the routing tables of otherdevices have to be updated before that. Also movements of the devicescause less signaling traffic. The signaling traffic is minimized becauseevery node does not need to be informed about the route to every othernode.

Advantageous further developments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greaterdetail on the basis of preferred embodiments with reference to theaccompanying drawings, in which:

FIG. 1 shows a schematic representation of a wireless mesh network;

FIG. 2A shows a schematic block diagram of a logical structure of awireless mesh network with layer 3 forwarding from a layer 3perspective;

FIG. 2B shows a schematic block diagram of a logical structure of awireless mesh network with layer 2 forwarding from a layer 3perspective;

FIG. 3 shows a routing example according to the preferred embodiments;

FIG. 4 shows a direction based packet routing according to a firstpreferred embodiment; and

FIG. 5 shows a distance based packet routing according to a secondpreferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will now be describedon the basis of a WMN as indicated in FIG. 1.

FIG. 2A shows a schematic block diagram of a conventional logicalstructure of a WMN with network layer forwarding from a network layerperspective. Here, the network layer routing protocols have to provideinformation required for packet routing inside the WMN, i.e. everywireless router has to know a functional route to every other wirelessrouter. The wireless routers WR are connected together with separatedlinks and the packets are routed between different wireless routersinside the WMN.

FIG. 2B shows a schematic block diagram of a logical structure of awireless mesh network with link layer forwarding from a network layerperspective, according to the preferred embodiment. Logically, from thenetwork layer perspective, the wireless routers WR form a network inwhich they are connected together with a single link. Link layerforwarding is much lighter and faster than network layer forwarding ifthe switching can be implemented with simple enough method. That is whylink layer forwarding consumes much less CPU power than network layerforwarding and the cost of the router is reduced considerably.

According to the preferred embodiment, a position or location based linklayer addressing (e.g. MAC addressing) and switching can be used in thelink layer forwarding to provide a simple addressing and routing method.Such a position-based method may enable faster, simpler and more optimalforwarding, thus reducing the cost of the wireless routers. Basicallylocation based addressing means that the link layer addressing is basedon the location of the devices. In other words the link layer address ofthe device tells its current location on the globe.

Due to the location based addressing at the link layer it can be seene.g. from the MAC-address where the devices are located related to otherdevices. When a network device compares the MAC-address of an incomingpacket to its own address it immediately knows in which direction thepackets destination node is located and it can forward the packetaccordingly. So there is no need for big routing tables, because onlythe addresses of the nearest neighbors have to be known.

FIG. 3 shows a routing example according to the preferred embodimentsbased on an WMN with seven nodes S and b to g. The node S at the left isa source node that wants to send a packet to node g at bottom rightcorner. The destination MAC-address is marked into e.g. an address fieldof the packet (e.g. MAC PDU) and thus tells the location of thedestination. So, the intermediate nodes c and e do not have to know thetopology of the network in order to route the packet to its destination,because they know the geographic location of the destination (from thedestination MAC-address) and their own geographic location. Thus, theycan route the packet into the right direction and finally the packetarrives at its destination node g.

The addresses used may be globally unique, or they may be unique only oncertain area or on certain type of network only. If addresses are uniqueonly on certain area they are all compared to the same fixed point.There may also be different methods how to derive the address from theposition. If more than one method is used simultaneously in the samenetwork there has to be a way to define which method is used in whichdevices.

The location information of a device may be derived using the alreadyexisting GPS system or some other known or future positioning orlocating techniques, e.g. positioning systems of GSM, which should worksomehow even indoors. Other future positioning systems with sufficientaccuracy might also be used. Devices can also use the information of thepositions of the neighbouring devices and the radio propagation delaysto the neighbors when calculating their own location. If the deviceknows the positions of its three neighbours and the distances to them,it can calculate its own location in two-dimensional space from thisinformation.

The packet forwarding in the WMN can be made using the position basedaddressing only or together with traditional routing methods combiningthe benefits of both approaches.

According to the preferred embodiments, packet forwarding or routing isdone entirely on layer 2. When a packet arrives to a node the nodederives from the destination MAC-address the location of the destinationof the packet.

In the first preferred embodiment, the direction of the destination isdetermined at a node based on its own exact location and the location ofthe destination. After that, the node forwards the packet to theneighbouring node, which is closest to that direction. Such a directionbased routing principle is shown in FIG. 4, where an initial node orwireless router 10 determines or calculates the direction of thedestination node 30 from its own position and the position of thedestination node, as derived from the corresponding MAC address of theMAC PDU. Then, it calculates the differences α and β between thedestination direction and the known directions of neighbouring nodes orwireless routers 20 and 40, respectively. Then, it selects theneighbouring node with the smaller difference and routes the packet tothis node, as indicated by the routing paths R in FIG. 4.

FIG. 5 shows alternative distance based routing, where the source node10 determines or calculates distances L, S between the destination node30 and all it's neighbouring nodes 20, 40 based on the derived positionof the destination node 30. Then it just forwards the packet to theneighbouring node that is closest to the destination node 30. In thepresent example of FIG. 5, the distance S between the lower neighbouringnode 40 and destination node is smaller, and the routing path R passesthrough the lower neighbouring node 40.

In some cases the above two alternative methods according to the firstand second preferred embodiment may lead to different kinds ofbehaviour, but in practice the difference should be minimal. The methodaccording to the first embodiment leads to shorter hops thus cuttingdown the power consumption because of less transmit power needed. Themethod according to the second embodiment leads to longer hopsminimizing the total amount of hops to reach the destination. But italso means that more transmit power is needed reducing the battery life,and other neighbouring devices are also disturbed more because of thehigher transmit power used.

It is noted that also other parameters may be taken into account whenmaking the forwarding or routing decision. These may include capacitiesof the links, bit error ratios, different loads on different links, andso on.

Because addressing is based on the location, the devices have to knowtheir current location all the time. The location information should beaccurate enough so that the forwarding is possible with it, but it isnot needed to be too accurate either.

Because all the nodes in a network know who their neighbours are, theexact location information is not needed anymore when packets get closeenough to their destination. This means that the accuracy needed is thesame as the distance of the neighbours. In addition, the accuracy doesnot need to be even that exact if it has been taken care that it is moreaccurate when comparing to the neighbours. In other words systematicerror in location information is not that critical. Systematic error canoccur for example when the location of a device is determined from thelocations of the neighbouring devices and from the distances to theneighbours.

Because the MAC-address of a device is based on the location of thedevice it has to be changed when the equipment moves. The changes in theaddress have to be told at least to the neighbours of the device so thatthey can forward the packets destined to the node correctly. This alsoaffects the routing of the other packets. Despite of the change in theaddress, the node may still receive packets with the old address forsome time. Moreover, the nodes with which the node has communicatedrecently could be informed about the address change in order to avoidpacket losses. There should also be specific nodes in the network towhom the MAC-addresses are told and from whom the MAC addressescorresponding to certain IP-addresses are asked. In other words thereshould be nodes acting as an neighbour discovery cache. So, one (thenearest) of these specific nodes is to be informed about the addresschange, after which the others can get the information from thisspecific node.

The address change is actually needed only when it has a significanteffect on routing. This means that if the moving node does not pass anyother nodes, the movement does not have very much effect on the routing.Actually, the system may be designed so that the neighbouring nodes knowthe locations of the node more precisely than the other nodes in thenetwork and the forwarding decision could be done according to thisinformation. The MAC address would be used only when making routingdecisions more far away from the node and therefore MAC address has tobe changed only when the neighbourhood changes (node passes other nodes,new neighbours found). Nodes that are moving with constant speed mayalso predict their future movement and start the address change processin advance.

The packet is switched through the network until it reaches itsdestination or the switching algorithm can not conclude where to sendthe packet next. In these situations the packet is passed to the upperprotocol layer (network layer), which then decides what to do with thepacket. The situations where the switching algorithm has to pass thepacket to the upper layer and the operations performed by the node ifthe packet did not reach the destination with the normal forwardingmethods are defined in the following.

The packet that reached its destination in the link layer is processedaccording to the normal router operation at the IP level. The link layerdestination is not of course necessarily the destination of the IPpacket but can be a router in the middle of the route in the network. Ifthe source and the destination of the received IP packet are at the samenetwork, the packet is normally forwarded and also a (ICMP/neighbourdiscovery protocol) redirect message may be used to tell the source tosend the packet directly to the MAC address of the destination.

There are at least three situations where the switching algorithm failsto deliver the packet to its destination and where the packet has to bepassed to the upper layer:

-   -   1) the destination does not exist,    -   2) it cannot be heard because of a radio interference, or    -   3) there is no direct route to the destination.

The switching algorithm can detect these situations from twoindications:

-   -   1) the packet is coming from an interface to which it should be        sent according to the switching algorithm, or    -   2) the wireless router can hear another wireless router located        behind the destination wireless router but it cannot hear the        destination itself.

MAC address resolution can be done in IPv4 and IPv6 networks by usingthe Address Resolution Protocol and the Neighbour Discovery Protocol,respectively. In the WMNs, these protocols consume too much bandwidthbecause of their broadcast and multicast MAC address usage. That is whythese packets may only be delivered to certain selected nodes, whichthen proxy the information to the ones that requested it. The node, thatrelays the multi- and broadcast packets to the selected node, may alsointercept the packets and act as a proxy for a while. The selected nodesthen keep the information up-to-date between themselves. If theseselected nodes are connected to some core network, it can be used forinformation updating instead of the WMNs. Other protocols that usemulti- and/or broadcast messages may also be implemented by using themethod described above. If a node changes its location inside the WMNand its GPA based MAC address changes, it reports the new MAC address toa selected node and/or also to all the other nodes it has communicatedrecently with inside the WMN, and/or to any other network node. Becausethe MAC address of a node may change in the WMN frequently, the MACaddresses of the nodes can not be cached for a long time by the othernodes. A node should accept packets coming with the old MAC address(es)as long as the other nodes might cache the address. Of course if a nodechanges its location quickly enough a packet may not find itsdestination with the old MAC address. In that case the packets arererouted to the new location or dropped by the neighbour routers in theprevious location or by any other network node. In order to enable thererouting the node may report its new MAC address also to all theprevious neighbours it cannot hear anymore.

It should be noted that the present invention is not restricted to aposition based MAC addressing. Implementations of the invention in othersystems are also possible, where position or location based changeableaddresses can be provided on a lower protocol level, while static ornon-changeable addresses can be provided on a higher protocol level.

1. A method, comprising: adding to a packet an address information of aprotocol layer lower than a network layer, the packet comprising anInternet Protocol address and the address information, the InternetProtocol address represents a network layer address, the added addressinformation representing a geographical location of a final destinationnode to which the packet is to be routed, the added address informationis configured to be changed during forwarding of the packet through awireless network when the geographical location of the final destinationnode changes; and forwarding the packet within the wireless network tothe final destination node based on the added address information of thelower protocol layer by routing based on a difference between thegeographical location of a present node and the final destination node,the Internet Protocol address used to route the packet when the packetreaches at least one of the final destination node or a switchingalgorithm using the added address information does not yield where toforward the packet, wherein the packet is passed to a higher protocollayer when at least one of the following occurs: the final destinationnode does not exist within the wireless network, the final destinationnode cannot be heard, or when there is no direct route within thewireless network to the final destination node, and wherein the networklayer is configured to drop the packet, when the packet is passed to thenetwork layer.
 2. A method according to claim 1, wherein said differencebetween said present node and said final destination node is determinedby calculating differences between the direction of said finaldestination node and the directions of neighboring nodes.
 3. A methodaccording to claim 1, wherein said difference between said present nodeand said final destination node is determined by calculating distancesbetween said final destination node and neighboring nodes.
 4. A methodaccording to claim 1, wherein said address information is a link layeraddress.
 5. A method according to claim 4, wherein said link layeraddress is a medium access control address.
 6. A method according toclaim 1, wherein said network layer is an internet protocol layer.
 7. Amethod according to claim 1, wherein a new lower protocol layer addressis reported to neighboring nodes, to nodes which have been communicatedto recently and/or any other nodes in the network, when the geographicallocation of a network node changes.
 8. A method according to claim 1,wherein said lower protocol layer address is a location based address.9. A method according to claim 1, wherein said packet is rerouted ordropped by a neighboring or any other node when an old lower protocollayer address cannot be located anymore.
 10. An apparatus, comprising: aprocessor configured to add to a packet an address information of aprotocol layer lower than a network layer, the packet comprising anInternet Protocol address and the address information, the InternetProtocol address represents a network layer address, the added addressinformation representing a geographical location of a final destinationnode to which said packet is finally to be routed the added addressinformation is configured to be changed during forwarding of the packetthrough a wireless network when the geographical location of the finaldestination node changes; and a transmitter configured to forwarding thepacket within the wireless network to the final destination node basedon the added address information of the lower protocol layer by routingbased on a difference between the geographical location of a presentnode and the final destination node, the Internet Protocol address usedto route the packet when the packet reaches at least one of the finaldestination node or a switching algorithm using the added addressinformation does not yield where to forward the packet, wherein thepacket is passed to a higher protocol layer when at least one of thefollowing occurs: the final destination node does not exist within thewireless network, the final destination node cannot be heard, or whenthere is no direct route within the wireless network to the finaldestination node, and wherein the network layer is configured to dropthe packet, when the packet is passed to the network layer.
 11. Anapparatus according to claim 10, wherein said difference between saidpresent node and said final destination node is configured to bedetermined by calculating differences between the direction of saidfinal destination node and the directions of neighboring nodes.
 12. Anapparatus according to claim 10, wherein said difference between saidpresent node and said final destination node is configured to bedetermined by calculating distances between said final destination nodeand neighboring nodes.
 13. An apparatus according to claim 10, whereinsaid address information is a link layer address.
 14. An apparatusaccording to claim 13, wherein said link layer address is a mediumaccess control address.
 15. An apparatus according to claim 10, whereinsaid network layer is an internet protocol layer.
 16. An apparatusaccording to claim 10, wherein said apparatus is configured to report anew lower protocol layer address to neighboring nodes, to nodes whichhave been communicated to recently, and/or any other nodes in thenetwork, when the geographical location of a network node changes. 17.An apparatus according to claim 10, wherein said lower protocol layeraddress is a location based address.
 18. An apparatus, comprising:adding means for adding to a packet an address information of a protocollayer lower than a network layer, the packet comprising an InternetProtocol address and the address information, the Internet Protocoladdress represents a network layer address, the added addressinformation representing a geographical location of a final destinationnode to which the packet is to be routed, the added address informationis configured to be changed during forwarding of the packet through awireless network when the geographical location of the final destinationnode changes; and forwarding the packet within the wireless network tothe final destination node based on the added address information of thelower protocol layer by routing based on a difference between thegeographical location of a present node and the final destination node,the Internet Protocol address used to route the packet when the packetreaches at least one of the final destination node or a switchingalgorithm using the added address information does not yield where toforward the packet, wherein the packet is passed to a higher protocollayer when at least one of the following occurs: the final destinationnode does not exist within the wireless network, the final destinationnode cannot be heard, or when there is no direct route within thewireless network to the final destination node, and wherein the networklayer is configured to drop the packet, when the packet is passed to thenetwork layer.